1. Field of the Invention
The present invention relates to an expander for radially expand tubular elements.
2. Description of the Prior Art
A conventional expander for tubular elements are disclosed in TWI320459, U.S. Pat. No. 3,077,916, or U.S. Pat. No. 4,530,231. Two conical clamping elements are arranged correspondingly, and a plurality of expanding pieces are arranged around conical faces of the clamping elements. When the distance between the two clamping elements, the expanding pieces are radially pushed outward by the conical faces, and a wall of the tubular element is expanded outward.
Generally, the two clamping elements are screwed with a threaded rod. The two clamping elements approach or move away from each other when the threaded rod is rotated. More specifically, one of the clamping elements rotates with the threaded rod, and another of the clamping elements rotates relative to the threaded rod. That is, the two conical faces rotate relative to each other. However, the expanding pieces abut against the two conical faces, so the expanding piece may possibly expand unevenly when the two conical faces rotate with respect to each other. As a result, the expanding pieces are possible to be damaged.
To prevent the problems mentioned above, the expanding pieces are disposed on one of the clamping elements. By the clamping element fixing, the expanding pieces are prevented from distortion. For instance, the conical face of one of the clamping elements is formed with a plurality of ribs spacedly arranged, or the conical face is formed as a pyramid. The ribs or the edges are located between any two expanding pieces to prevent the expanding pieces from rotating relative to the conical faces. However, the ribs abut against the edges of the expanding pieces, so force is unable to be distributed evenly on the expanding pieces. Also, the edges of the expanding pieces may be abraded. Furthermore, because torque in a fixed direction is exerted on the expanding pieces, the abrasions at two sides of the expanding pieces are uneven. After using for a long time, the shape of each expanding piece is not symmetrical anymore.
Besides, a tool for extracting a tubular element having a similar structure as the expander is disclosed in U.S. Pat. No. 4,104,775. However, the expanding pieces are not fastened together and are possible to fall down. Also, the guiding slots are formed on the inner face of the expanding piece, so the expanding piece has smaller thickness and weak structure strength. To work on tubular elements extraction, the expanding piece standing smaller force is still functional. However, to work on tubular elements expansion, the expanding piece standing larger force may be unfunctional or damaged. If increasing the thickness to improve structure strength, the expanding pieces are difficult to be inserted into smaller tubular elements.